Can a dinosaur get lucky through mass extinction? Apparently the answer is yes, at least according to a paper published in Science.
In this paper Stephen Brusatte, of the American Museum of Natural History, and colleagues report that the dinos were lucky. Specifically, they found that the reason dinosaurs prospered at the expense of crurotarsan archosaurs (crocodiles’ great-to-the-power-n ancestors) was probably luck.
“If we were standing in the Late Triassic, 210 million years ago or so, and had to bet on which group would eventually dominate ecosystems, all reasonable gamblers would go with the crurotarsans,” says Brusatte (press release from Bristol University, where much of the work was done).
The paper in Science compares the evolutionary rate and number of different types of dinosaurs with their major rivals the crurotarsan archosaurs, using remains of both. It shows the latter had a greater number of body types, diets, and lifestyles (and therefore possible niches they could fill) than dinosaurs. They also had a similar rate of evolution to dinos. It’s already known that crurotarsans were more abundant. In other words: they shouldn’t have lost this one.
The reason they did, says Brusatte, “is two mass extinction events: the dinosaurs not only got lucky, but they got lucky twice”.
First up: 228 million years ago the Carnian-Norian event took out many competitors of the dinosaurs but not the crurotarsans. Then 200 million years ago the Triassic extinction event took out most of the crurotarsans as well.
“Why did crurotarsans go extinct and not dinosaurs? We don’t know the answer to that, but we suspect that it was nothing more than luck, plain and simple,” says Brusatte.
Many paleontologists consider these findings a major step in dinosaur science. “It’s really refreshing,” says Kristi Curry-Rogers, a dinosaur paleontologist at Macalester College in Saint Paul, Minn. “It definitely challenges the standard story of dinosaur evolution…. In the world of dinosaurs, we see a lot that portrays them in ways that science doesn’t really follow.”
But not all experts agree. “I think that the conclusions of the authors aren’t warranted,” says Kevin Padian, a dinosaur paleontologist at the University of California, Berkeley. “Good luck isn’t an evolutionary force…. Extinctions aren’t random.” He believes that dinosaurs are different enough from crurotarsans that they may have had a competitive edge.
The crurotarsans were a fabulous bunch of monsters. Some called phytosaurs looked and lived a lot like today’s crocodiles, staying submerged in rivers or lakes until attacking a victim. The North American phytosaur Smilosuchus grew to 39 feet long.
Others called rauisuchians were land predators with four powerful legs, massive skulls and flesh-tearing teeth. South America’s Fasolasuchus grew to 33 feet long.
Both were far more impressive than the typical dinosaur predator of the time like Coelophysis, a relatively lightly built, two-legged hunter about 10 feet long.
Scientists long thought that dinosaurs achieved world domination through superiority: their evolutionary trajectory suggested they simply adapted better than those with which they were competing. But a new finding may take some of the shine off the origins of their 100-million-year reign.
Image: skulls of crurotarsan archosaurs / Steve Brusatte